Galvanizing solution for the galvanic deposition of copper

ABSTRACT

The invention relates to a novel galvanizing solution for the galvanic deposition of copper. Hydroxylamine sulfate or hydroxylamine hydrochloride are utilized as addition reagents and added to the galvanizing solution during the galvanic deposition of copper which is used in the manufacture of semiconductors.

This application is a 371 National Stage Application of PCT/EP/00/08312filed Aug. 25, 2000.

The present invention concerns to a novel electroplating solution forcopper electroplating. Hydroxyl amine sulfate or hydroxyl aminehydrochloride are used as additive agents and added into theelectroplating solution used in copper electroplating process ofsemiconductor manufacturing.

Low resistivity and expected good reliability of copper make it anobvious choice used for long and narrow interconnections. However,processing difficulties associated with Cu still need to be overcomebefore the introduction of Cu metallization. In addition, a commerciallymaturized equipment still needs to be developed in order to bring Cumetallization into production.

Via and trench will be filled copper by plating (also calledelectrochemical deposition). However, a major drawback of electrolesscopper deposition process is low plating rate. Other shortcomings, e.q.contamination, healthy, complex compounds, hard to control itscomposition are also to be considered. Electroplating is an attractivealternative for copper deposition, since it is not available fortungsten or aluminum. Electroplating is a very inexpensive processcompared to vacuum fabrication and electroless deposition. A number ofresearch groups have developed electroplating to use in damascenestructures. A potential disadvantage of electroplating is that it is atwo-step process. PVD or CVD method can be competed in one step(directly on top of the diffusion-barrier), while electroplatingrequires deposition of a thin seed-layer prior to the plating fill step.The seed-layer provides a low-resistance conductor for the platingcurrent that drives the process, and also facilitates film nucleation.If seed layer is not perfect (i.e., continuous), it can create a voidduring copper filling.

Copper is the most favorable material used for seed layer because of itshigh conductivity, and because it is an ideal nucleation layer with highconductivity. Copper seed layer plays two critical roles duringelectroplating. On the wafer scale, seed layer carries current from theedge of the wafer to the center, allowing plating current source tocontact the wafer only near the edge. The thickness of seed layer mustbe sufficient large so that voltage drops from wafer edge to center doesnot reduce electroplating uniformity. On a localized region, seed layercarries current from the top surface to the bottom of vias and trenches.When there is insufficient seed-layer thickness at the bottom, a void isformed at the center of via or trench during deposition. In order toproduce a uniform and good adhesion film of electroplated copper, a seedlayer must be deposited perfectly over the barrier layer.

In principle, the thickness of the seed layer at the bottom (in a highaspect ratio feature) can be increased by increasing the thickness ofcopper that deposited on the field. However, an excess of seed materialdeposited at the field level will pinch off the via or trench, creatinga center void in the film. Although PVD copper has poor step coverage ina high-aspect-ratio of vias and trenches, it has been successfullyapplied to Cu electroplating. PVD copper used for seed layer issuccessful at the narrowest feature of 0.3 μm. At the dimension below0.3 μm, PVD copper seed layer can be deposited using ionized PVDmethods. In addition, a CVD seed layer will probably be used for nextgenerations.

Copper CVD is good alternative used for seed-layer primarily because ithas nearly 100% step coverage. A superior step-coverage of the CVDcopper process requires no additional cost relative to the PVD process.CVD copper seed-layer process can be used to fill narrow via completelyin a single-damascene application, which is a significant process infuture technique.

Although electroplating is a two-step process, calculations indicatethat it offers a lower overall cost-of-ownership (COO) compared to CVD.The COO calculation includes the cost of the deposition equipment,fabrication space and consumables, but neglects device or process yield.The major difference is mainly due to lower capital and chemical costsof the electroplating process. Most importantly, a well-tunedelectroplating process can fill a high-aspect-ratio structures.

(III) Enhanced Gap Filing Capability in Electroplating

The big challenge in Damascene plating is to fill vias/trenches withoutvoid or seam formations. FIG. 1 presents possible evolution of platedcopper. In conformal plating, a deposit of equal thickness at everypoint of a certain dimension leads to the creation of a seam, or voidsform because of different deposition rate. Sub-normal plating leads tothe formation of a void even in straight-walled features. Sub-conformalplating is resulted from substantial depletion of the cupric ion in theplating solution inside the feature, which produces significantconcentration overpotentials to cause the current to flow preferentiallyto more accessible locations outside the feature. In order to getdefect-free filling, an increasing deposition rate along the sides andthe bottom of the feature is desired. As early as 1990 at IBM, theydiscovered certain plating solutions that contain additives could leadto super-conformal formation that eventually produces void-free andseamless structures [FIG. 1]. They call this is “super-filling”.

In generally, the electroplating rate is a direct function of currentdensity. If one has a high density at the top of a structure (or at thetop sharp edges) and a lower density at the bottoms one gets a differentplating rate. Voids form because there is faster plating on the topsharp edges of trenches compared to on the bottoms. Two methods toenhance deposition uniformity and gap filling capability inelectroplating process are physical and chemical approaches.

Physical method is to apply a pulsed plating (PP) or periodic pulsereverse (PPR) with both positive and negative pulses (etc., a waveformto the cathode/anode system). Periodic pulsed plating (PPR) techniquescould reduce the formation of voids because the rate of metal depositioninside a trench is nearly the same as the rate at the upper portion. Itis virtually like a deposition/etching sequence. It can produce adeposition/etching sequence that polish copper in the high-densityregions more quickly than in the low-density regions, and produce therequired gap fill capability. Pulsed plating (PR) can decrease theeffective mass transfer boundary layer thickness and thus produce higherinstantaneous plating current density as well as better copperdistribution. Decreasing thickness of boundary layer could lead tosignificant concentration overpotentials decreased. Therefore, thefilling capability could be enhanced in a high aspect ratio ofvia/trench.

Chemical method is to add organic additives in the electroplatingsolution. A widely used electroplating solution consists of manyadditive groups (e.g. thiourea, acetylthiourea, naphthalene sulfonicacid). However, levelers are chemicals with an amine group (e.g.tribenzylamine). Carrying agents could promote the deposition of ductilecopper, while brightener and leveling agents level out non-uniformsubstrates during electrodeposition. In order to make electrodepositionon a small dimension very well (in very high aspect ratios for futureULSI metallization), an understanding of additive agent is required tofurther study. Establishing proper agents in a specific action and aproper concentration ratio often determines the success of a gap fillingplating process.

In 1995, Intel corporation utilized a pulsed electroplating technologyin a damascene process to produce low resistance copper interconnectswith aspect ratios of 2.4:1.[FIGS. 3 a & 3 b.] A tantalum barrier layer(about 300-600 A thickness) and a copper seed layer were deposited usingcollimated PVD. Normally the thickness of the copper seed layer was 1100A on the top of the substrate, 280 A on the sidewall and 650 A on thebottom of the trench. After electroplating of about 1.5-2.5 μm of copperat a rate of 500-2000 A/min, the samples were processed by chemicalmechanical polishing to remove the field metallization and leave copperin the trenches and vias. The resistivity of electroplated copper waslower than 1.88 μΩ·cm. They demonstrated that the filling capability washeavily dependent upon the sputtered copper uniformity in the trenches.If sputtered copper coverage showed a significant closure at the top ofthe trench, then large voids could be formed after plating. However, ifa uniform copper were sputtered in the trenches, then a good copperfilling would occur during plating. In addition, an inadequate waveformcontrol could result in severe void under the identical sputtering andplating condition.

In 1998, CuTek Research Inc. developed a new deposition system, whichhas a standard cluster tool configuration with a fully automaticdry/clean wafer in and dry/clean wafer out operation. Cu electroplatingis performed on a Cu seed layer with a thickness of 30-150 nm. Asputtered Ta or TaN with 30 nm thickness is used as a barrier and anadhesion layer, respectively. An excellent gap filling with thickerdeposited in the trenches than on top of the field surface could beachieved using pulse plating (PP) and periodic pulse reverses (PPR) withsuitable additive agents. Dual damascene structures with 0.4 μm featuresize in an aspect-ratio of 5:1 and deep contact structures with 0.25 μmfeature size in an aspect-ratio of 8:1 could be completely filledwithout any void or seam function. The impurity contained inelectroplated Cu film is measured to be below 50 ppm. The majorcontaminants found were H, S, Cl, and C. A higher concentration of theseelements is measured at the edge of wafer in comparison with the center.This is probably due to high hydrogen evolution and higher organicadditive incorporated at the high current density region.

In 1998, UMC (Uited Miroelectronics Corporation) has demonstrated theintegration of copper process by using a simple and cost-effective dualdamascene architecture. The metal-filling process for Cu interconnectionincludes (1) a deposition of 400 A ionized-metal-plasma (IMP) Ta or TaNwhich serves as barrier to prevent Cu diffusion and as an adhesionpromoter of Cu to oxide IMD layer, (2) a PVD Cu seed layer, and (3) a Cuelectroplating. An excess of Cu over oxide is removed by usingchemical-mechanical polish (CMP) technique. The optimized metaldeposition process is able to fill a high aspect-ratio (˜5) of a 0.28 μmfeature hole without seams formation.[FIG. 4]

(VI) EXPERIMENT [A] Basic

Two major components in the electroplating process are compositions ofthe electroplating solution and the method in which the current applied.In section (I), we have discussed how to select the method of currentapplied and the composition of electroplating solution. In addition, itis noticed that the electrolytic production of copper in copperdeposition and the control of the cathode growth are very important. Thereason is important because cathode growth is affected by many factors:(a) the quality of anode, (b) the electrolyte composition andimpurities, (c) the current density. (d) The surface condition of thestarter cathode, (e) the geometric anode and cathode (f) the uniformityof spacing (agitation) and the distance between electrodes and (g) thetemperature or current density.

Electroplating can be carried out at a constant current, a constantvoltage, or at variable waveforms of current or voltage. In ourexperiment, a constant current with accurate control of the mass ofdeposited metal is most easily obtained. Plating at a constant voltagewith viable waveforms requires more complex equipment and control. Thetemperature of electroplating solution in experiment process is constant(at R.T). Therefore, we can neglect the influence of temperature ondeposition rate and film quality.

[B] Prepare Substrate and Experimental Process

P-type (001) oriented single crystal silicon wafers of 15-25 Ω-cm in6-inch diameter were used as deposition substrates in this work. Theblank wafers were first cleaned by a conventional wet cleaning process.After wet cleaning, wafers were treated with a dilute 1:50 HF solutionbefore loading into a deposition chamber. A 50-nm-thickness of TIN and a50-nm-thickness of Cu were deposited using conventional PVD to act as adiffusion barrier and a seed layer, respectively. Patterned wafers werefabricated to examine the ability of Cu electroplating in small trenchesand vias. After standard RCA cleaning, wafers were treated with thermaloxidation. Then, a photolithography technique with reactive ion etching(RIE) was used to define a definite dimension of trenches/vias. A40-nm-thickness of TaN used as barrier and a 150-nm-thickness of Cu usedas a seed layer were deposited by ionized metal plasma (IMP) PVD,respectively. The dimension of trench/via was defined between 0.3-0.8μm. An electroplating solution, which was used for Cu electroplating,was usually composed of CuSO₄.5H₂O, H₂SO₄, Cl, additives, and wettingagent. The compositions of the electroplating solution were described inTable 2. Additives were frequently added in Cu electroplating becausethey worked as brightening, hardening, grain refining, and levelingagents. The current density applied was 0.1-4 A/dm². Besides, Cu(P) (Cu:99.95%, P: 0.05%) material was used as an anode to supply sufficient Cuions and made good quality of Cu electroplated films.

[C] Equipment of Electroplating

The simple electroplating system was described as followed: [FIG. 5]

-   (a) Wafer: P-type (001) oriented single crystal silicon wafers of    15-25 Ω-cm 6′-inch diameter-   (b) Power Supplier: GW1860 ()-   (c) PP Tank: 20 cm×19 cm×20.5 cm-   (d) Rolled Copper (Cu: 99.95%, P: 0.05%): 30 piece    -   Produced by Meltex Learonal Japan company-   (e) Titanium anode basket: 20 cm×19 cm×2 cm

[D] Analysis Tool

(a) Field Emission Scanning Electron Micrscopy (FESEM):

HITACHI S-400

The morphology and step coverage we examined by using field emissionscanning electron microscope (FESEM).

(b) Sheet Resistance Measurement

The resistivity of electroplated Cu film was measured by a four-pointprobe. The sheet resistance of the Cu films were determined using astandard equal-spaced four point probe. The spacing between equal-spacedfour point probes was 1.016 mm. Current was passed through the outer twoprobes and the potential across the inner two probes was measured. Theapplied current was from 0.1 to 0.5 mA.

(c) X-Ray Power Diffractometer (XRPD): MAC Sience, MXP18

X-Ray diffractometer (XRD) was utilized to investigate crystalorientation of Cu electroplated films. X-ray analysis was performed in aShimadzu diffractometer and employed with Cu K α radiation (λ=1.542 A)in conventional reflection geometry and scintillation counter detection.

(d) Auger Electron Spectrocope (AES): FISONS Microlab 310F

Auger electron spectroscope (AES) was applied to determine thestoichiometry and uniformity along the depth direction.

(e) Secondary Ion Mass Spectrometry (SIMS); Camera IMS-4f

SIMS (Secondary Ion Mass Spectrometry) was utilized to do thecontamination analysis.

(VII) Results and Discussions [A] The Effect of Applied Current andConcentration

In our study, we first change the concentration of sulfate acid and keepconcentration of copper sulfate at constant. FIG. 6 shows theconcentration change of sulfate acid vs. thickness variation. We canfind no obvious change in thickness when increasing the concentration ofsulfate acid. FIG. 7 presents the relationship between film resistivityand concentration of H₂SO₄. The resistivity is constant whenconcentration is increasing. In FIGS. 8(a) & 8(b), SEM images show filmmorphology with and without H₂SO₄ presence. We can find the uniformityand roughness of copper film is smoother when the sulfate acid inpresent and makes the resistivity of copper film lower. In our opinion,the purpose of sulfuric acid is to prevent anode polarization and toimprove conductivity of the electrolyte and cathode film, but does notvery strong affect on the deposited copper film.

In experiment, we keep concentrations of sulfate acid (=197 g/l) andsulfate copper (90 g/l) constant. Since conductivity of solutions ishigher, and anode and cathode polarization are small, voltage requiredfor Cu deposition is small. Change in sulfate acid concentration hasmore influence than changes in copper sulfate concentration in solutionconductivity and anode and cathode polarization. FIG. 9 shows therelation between applied current change and Cu deposition rates. It isfound that deposition rate increases with increasing applied current.The deposition rate reaches a maximum when applied current increases to3.2 A/dm². As shown in FIG. 10, we can see the resistivity changes withdifferent applied current. When applied current is at 3.2 A/dm², theresistivity becomes very large. FIGS. 11(a) and 11(b) present filmmorphology of Cu electroplated on seed layer/TiN/Si at various currentdensities (1-4 A/dm²) without additive addition. Large grain of Cu filmis observed at high current density. The resistivity exhibits unusuallyhigh (˜10 μm-cm) when high current is applied. A high resistivity of Cufilm observed could be attributed to rough surface formation, whichresulted in film non-conformity at high current condition. The roughsurface formed at high current could be rationalized by followingpostulations. It was supposed that Cu electroplating rate depended on Cuions diffusion onto a substrate surface. At high current applied, mostof Cu ions were effected at a high electric field; therefore, Cu ionsdiffusion from solution to substrate surface was very fast. Since Cu iondiffusions was very fast, the depletion of Cu ions in diffusion layerwas very rapid; Cu ions could not be supplied instantly fromelectroplated solution into a diffusion layer. The Cu electroplating waslimited by Cu ion diffusion. This was called diffusion controlled. Sinceno replenish of Cu ions diffused onto substrate surface, no more ofnucleation was formed on the surface. Cu aggregation could occur on thesurface due to high electric field effect. A rough surface formed wasascribed to Cu agglomeration. FIG. 12 presents relative intensity ratioof Cu(111)/Cu(002) by X-ray diffraction measurement at various appliedcurrent density. According to XRD results, a strong (111) orientationwas always observed at higher current density applied. The developmentof growth orientation of the copper film could be rationalized byconsidering surface energy and strain energy at different crystalorientations. In the initial stage, the orientation of Cu (002) planewas formed because this plane possessed the lowest surface energy. Asapplied electrical current was increased, the strain energy becomes adominant factor in governing grain growth. The peak intensity of Cu(111) was increasing at high electrical current applied because of highstrain energy in Cu (111) orientation. In addition, a Cu (111)orientation was preferred because this orientation showed betterelectromigration resistance. Contradictory, Cu (111) formed at highcurrent density could make a surface rougher as shown in FIG. 16(b). Inorder to improve the filling of Cu electroplating, it was attempted toadd some additives in electroplating solution. A high resistivity of Cufilm at high current was also analyzed by SIMS and compared with that atlow current condition (see FIGS. 13 a & b). The oxygen concentration inthe high resistivity of Cu film is higher because of its rough surfacewith film non-conformity at high current condition.

[B] The Effect of Traditional Additive Agents

In order to understand the gap filling capability in electroplatingprocessing. Then, the dimension of trench/via was defined between0.30-0.8 μm used to test gap filing capability. FIG. 14 shows the imagesof pattern wafer before electroplating. The thickness of Cu seed layeron the bottom and on the side-wall is less than on the top.

We used HCl as additive agent for electroplating. Addition of HCl doesnot make any prominent difference in film resistivity and filmmorphology in blanket wafer.[FIG. 15] As shown from in pattern wafers[see FIGS. 16(a) and (b)], we find the uniformity at the top of thetrench is smoother when the HCl was added in solution. FIG. 17 revealedthat voids are formed if no additive agent was added into the solution.

Various organic and inorganic additives are added in solution to help Cuelectroplating. Thiourea is a common additive, which usually added inelectroplating solution. As presented in FIG. 18, the resistivity ofelectroplated Cu films does not show big difference when theconcentration of thiourea is smaller than 0.054 g/l. A high resistivityis observed when thiourea is more than 0.054 g/l. FIG. 19 presents theSEM image of Cu (111) at 0.03 g/l of thiourea addition. The current isapplied at 2.4 A/dm². As shown from SEM image, addition of additivescould help (111) formation at low current density, because the additivecould be incorporated into the deposit to provide a specific growthorientation. FIG. 20 presents the SEM image of the electroplated Cu filmat 0.054 g/l of thiourea addition. The current applied is still to keepat 2.4 A/dm². As shown in FIG. 20, when concentration of thiourea isincreasing, the dendrite produced during Cu electroplating isincreasing. This dendrite has similar geometric structure withdiffusion-limited clusters. Moreover, thiourea could decompose to formpernicious product (NH₄SCN) which results in embattlement ofelectroplated Cu films. FIG. 21 shows the resistivity of copper filmchange with deposition time. It is appeared that resistivity is lowerwhen the copper film become large block. Because that the grain boundaryof copper film is decreasing to make surface more smooth than initialthin film. The resistivity of Cu film is higher when thiourea is added.According to SIMS results [FIGS. 22(a)(b)(c)], we can find theconcentration of S element is increased with increasing concentration ofthiourea. It is suggested that thiourea adsorbed on the surface of thecathode could make the resistivity of Cu increasing. In addition, voidsis are formed when thiourea is used as additive agent.

PEG (polyethylene glycol) is widely used in Cu electroplating as acarrier agent. In this study, we use different molecular weight of PEG(200˜10,000) and added in electrolyte with HCl and small amount ofthiourea (0.0036 g/l), since small amount thiourea could help (111) planformation. We can determine the larger molecular weight (m.w.>200) makethe higher resistivity of copper film. According to FIG. 23, theresistivity of copper film is increasing with PEG molecular weighthigher with deposition time. It is suggested that the longer chainlength with thiourea is absorbed on the surface of the substrate. FromSEM image shown in FIGS. 24(a)(b), film morphology doesn't change a lotwhen PEG molecular weight is increasing, but the plane (111) isdecreasing when PEG molecular weight is increasing. [FIG. 25] Accordingto SIMS analysis [shown in FIGS. 26(a)(b)], the major components of Cufilm are still Cu, O, C, S and Ti. The amount of S element will beincreasing with increasing molecular weight of PEG. This observation isproved by our suggestion which discussed previously.

Based on our results, a lot of thiourea and larger molecular weight ofPEG (m.w>200) could not be used as additives in Cu electroplating forfuture Cu interconnect because of higher resistivity of copper film andpoor cap-filling ability. In order to make Cu electroplating implementedin ULSI processing, a suitable additive must be developed. In thisstudy, we try new traditional additive agents of molasses which showsthe same effect on resistivity of copper film.

Glucose is also a common traditional additive agent used in Cuelectroplating. In our experiment, we found the resistivity andorientation of electroplated copper film do not obviously change withdifferent amount of glucose. However, filling capability in via andtrench is poor. Although an equal thickness at all points of a featureis formed, a void still appears in the trench.

[C] The Effect of New Additive Agents

Sulfamates have been studied in interaction with a number of metals.They show little tendency to form complex in or affect the deposition byadsorption or bridging effects. Sulfamates could be used as agap-filling promoter in Cu electroplating because it could decreasecurrent efficient in Cu deposition. Since hydroxyl amine sulfate(NH₂OH)₂.H₂SO₄ has a similar functional group with sulfamate, it ispostulated that it could be act as a good gap filling promoter. In orderto examine if hydroxyl amine sulfate could act as a gap fillingpromoter, Cu electroplating with addition of hydroxyl amine sulfate isinvestigated in this experiment. The experiment is executed on thesubstrates with 0.3-0.8 μm width of trench/via. Since the thickness ofbase layer (seed layer and diffusion barrier) is 60 nm on the bottom andon the side wall and 120 nm on the top, the width less than 0.25 μmcould be electrodeposited in the 0.35 μm width of trench. FIG. 27reveals void is formed if no additive is added into the solution. Thedimension of trench in FIG. 31 is measured to be 0.4 μm. Since Cureduction is preferred to occur at the region of high current (at thetop of trench), a void is easy to form. No void formation is observedwhen the additive of (N₂OH)₂.H₂SO₄ is added into the electroplatingsolution, as shown in. FIG. 28. The dimension of trench is measured tobe 0.3 μm. A complete picture of SEM image in low magnification of Cuelectroplated on 0.3-0.8 μm of trench/via is presented in FIG. 29.According to previous results, it is demonstrated that Cu could beelectroplated into fine trenches or small sizes of vias when hydroxylamine sulfate is used as a gap filling promoter. In addition, theresistivity of Cu film does not show significant change. [see FIG. 30]The concentration of O in the Cu film measured to be very low [FIG. 31].Therefore, oxidation of Cu or seed layer could be neglected. Accordingto SIMS analysis, it is found that the concentration of impurity (Selement) is very low in copper film [FIG. 32]. A further study of thisnew additive is still investigated in progress.

Since hydroxyl amine sulfate ((NH₂OH)₂.H₂SO₄) has both amino and sulfatefunctional group, it is proposed to use as a gap filling promoter inhelping Cu electroplating. Another additive agent, hydroxyl aminehydrochloride (NH₂OH).HCl, could be considered to use for Cuelectroplating because it has a similar amine functional group withchloride. In our experiment, we use different amount of hydroxyl aminehydrochloride (NH₂OH).HCl as a gap filling promoter. The ability offilling is not really good. Some trenches can be completely filled by Cubut others can not. However, the lower resistivity of copper film couldbe decreased to 1.9 μΩ·cm when small or hydroxyl amine hydrochloride isused in the electrolyte compared to the Cu film with no additive added.[FIG. 30]

Other organic additives with unsaturated π bonds, like tribenzylamine,benzotriazole and naphthalene sulfonic acid, could be considered to beused as additives in Cu electroplating. Since they have unsaturated πbonds, the π electrons could interact with surface atoms of copper, toproduce substantial effect on the properties of deposits. Brightness,leveling, as well as stability effect is still needed to do furtherstudy. This study, we try to use tribenzylamine and benzotriazole asleveling agents. However, these levels agents are quite difficult insoluble in sulfate acid solution to make experiment unworkable.

(VIII) Conclusions

A strong Cu (111) peak was observed at higher electrical currentapplied. The development of growth orientation of the copper film couldbe rationalized by considering surface energy and stain energy atdifferent crystal planes. In the initial stage, the orientation of Cu(002) plane was existed because this plane possessed the lowest surfaceenergy. As applied electrical current was increased the stain energybecomes a dominant factor in governing grain growth. A strong peak of Cu(111) was appeared when applied electrical current was increasing. Inaddition, additives played an important role in controlling theorientation of electroplated Cu films at low current density. No voidformation was observed when Cu electrodeposited onto a 0.3 μm width oftrench in the presence of ((NH₂OH)₂.H₂SO₄) additive. The concentrationof O in the sample was measured to be rather low. Therefore, oxidationof Cu or seed layer could be neglected. In summary, sulfamate groupshowed little tendency to form complex ions, therefore, it couldstabilize Cu (I) and reduce current efficiency for copper deposition.Since hydroxyl amine sulfate ((NH₂OH)₂.H₂SO₄) had both amino and sulfatefunctional groups, which were similar to sulfamate, it was postulatedthat hydroxyl amine sulfate could be used as a gap filling promoter inhelping Cu electroplating.

TABLE I Chemical composition of the electroplated Cu solutionComposition Concentration CuSO4 5H2O 60-150 g/l H2SO4 80-150 g/l Cl ions50-150 ppm PEG ˜100 ppm Addition agents Small

Table Captions

Table 1. Chemical composition of the electroplated Cu solution

Figure Captions

FIG. 1. Typical deposition profile in plating.

FIG. 2. Schematic cross-section shows micro-roughness at cathode. Theleveling is accumulated at peak (P) because diffusion is relatively fastat the short distance from the diffusion boundary. Diffusion at valley(V) is too slow to keep up with consumption of leveling agent.Consequently, metal deposition is inhibited at peak but not in thevalleys, and filling in the valleys produces a smoother surface.

FIG. 3.(a) Copper electroplated into a 0.4 micron trench with aspectratio =2.1:1

FIG. 3.(b) Copper electroplated into a 0.35 micron trench with aspectratio =2.4:1

FIG. 4. The optimized deposition process is able to fill a highaspect-ratio (˜5) feature hole of a 0.28 μm via size without obviousseam formation.

FIG. 5. Schematic of the Cu electroplating system.

FIG. 6. Dependence of the thickness vs. H₂SO₄ concentration change.(CuSO₄.5H₂O at 90 g/l, current density at 2.4 A/dm² and time at 2 min)

FIG. 7. Cu films resistivity change as a function of concentration ofH₂SO₄ (CuSO₄.5H₂O at 90 g/l, H₂SO₄ at 90 g/l, current density at 2.4A/dm² at 2 min).

FIGS. 8 a and 8 b SEM images of copper film morphology with an withoutH₂SO₄ presence. (a) only CuSO₄.5H₂O (90 g/l) (b) CuSO₄.5H₂O (90 g/l) &H₂SO₄ (20 ml/l)

FIG. 9. Dependence of film deposition rate vs. current densityvariation. (CuSO₄.5H₂O at 90 g/l, H₂SO₄ at 197 g/l and time at 2 min)

FIG. 10. Film resistivity change as a function of applied currentvariation. (CuSO₄.5H₂O at 90 g/l, H₂SO₄ at 197 g/l and time at 2 min)

FIGS. 11 a and 11 b Cu film morphology at different applied currents.

FIG. 12. XRD measurement at various applied currents. (CuSO₄.5H₂O at 90g/l, H₂SO₄ at 197 g/l and time at 2 min)

FIG. 13.(a) The SIMS results showed that oxygen concentration inelectroplated Cu film at low applied current density of 1.2 A/dm².

FIG. 13.(b) The SIMS results showed that oxygen concentration inelectroplated Cu film at high applied current density of 3.2 A/dm².

FIG. 14 Showed the images of pattern wafer before electroplating

FIG. 15 The relationship of Cu film resistivity vs. variousconcentration of HCl (CuSO₄.5H₂O at 90 g/l, H₂SO₄ at 197 g/l, currentdensity at 2.4 A/dm² at 2 min).

FIGS. 16 a and 16 b The uniformity at the top of the trench is (a) notsmooth without HCl addition (b) more smooth with HCl addition.

FIG. 17 Voids are obviously formed in the trench without any additiveagent addition

FIG. 18 The relationship of Cu film resistivity vs. variousconcentration of (NH)₂CS. (CuSO₄.C⁵H₂O at 90 g/l, H₂SO₄ at 197 g/l, HClat 70 ppm, current density at 2.4 A/dm² at 2 min).

FIG. 19 SEM image of the electroplated Cu film at 0.03 g/l of thioureaaddition, applied current density is 2.4 A/dm².

FIG. 20 SEM image of the electroplated Cu film at 0.054 g/l of thioureaaddition, applied current density was 2.4 A/dm².

FIG. 21 The relationship of Cu film resistivity vs. deposition time((CuSO₄C₅H₂O at 90 g/l, H₂SO₄ at 197 g/l, HCl at 70 ppm current densityat 1.2 A/dm²).

FIG. 22(a) SIMS analysis on Cu film without thioura presence

FIG. 22(b) SIMS analysis on Cu film with thioura 0.0036 g/l addition

FIG. 22. (c) SIMS analysis on Cu film with thioura 0.018 g/l addition.

FIG. 23 The resistivity of Cu films change with various PEG molecularweight at different deposition time. (CuSO₄.5H₂O at 90 g/l, H₂SO₄ at 197g/l, HCl at 70 ppm, current density at 1.2 A/dm².

FIG. 24 Film morphology analysis with different amount of thiourea.

FIG. 25 XRD measurement at various PEG molecular weight.

FIG. 26(a) The SIMS analysis on Cu film with thiourea and PEG200addition.

FIG. 26(b) The SIMS analysis on Cu film with thiourea and PEG4000addition.

FIG. 27. The SEM image of the electroplated Cu film without additiveagent addition. The dimension of trench is 0.25 μm.

FIG. 28. The SEM image of the electroplated Cu film at 0.06 g/l of(NO₂OH)H₂SO₄ addition. The dimension of trench is 0.25 μm.

FIG. 29.(a) & (b) A low magnification of the SEM image of CuElectroplate on 0.3˜0.8 μm of trench/via.

FIG. 30. The resistivity change with different amount of additiveadditive agent at different deposition time.

FIG. 31. The AES analysis of the Cu film at 0.06 g/l of (NH₂OH)₂H₂SO₄addition.

FIG. 32. The SIMS analysis on Cu film at 0.06 g/l of (NO₂OH)₂H₂SO₄addition.

1. An electroplating solution for copper comprising CuSO₄.5H₂O, H₂SO₄,HCl, polyethylene glycol with a molecular weight greater than 200,hydroxyl amine sulfate, and hydroxyl amine chloride.
 2. Anelectroplating solution according to claim 1 further comprising Cl⁻ ionsin a range of 50-150 ppm and wherein the hydroxyl amine sulfate is in arange of 0.01-5 g/l.
 3. An electroplating solution according to claim 1further comprising Cl⁻ ions derived at least from the HCl in a range of55-125 ppm.
 4. An electroplating solution according to claim 1, furthercomprising an additive.
 5. An electroplating solution according to claim4, wherein the additive is thiourea, molasses, glucose, tribenzylamine,benzotriazole, or naphthalene sulfonic acid.
 6. An electroplatingsolution comprising adding together: CuSO₄.5H₂O; H₂SO₄; HCl; optionallyan additive; and polyethylene glycol with a molecular weight greaterthan 200, and either hydroxyl amine sulfate or hydroxyl amine chloride.7. An electroplating solution comprising: CuSO₄.5H₂O; H₂SO₄; Cl⁻ ions;polyethylene glycol with a molecular weight greater than 200; andhydroxyl amine sulfate or hydroxyl amine chloride.
 8. An electroplatingsolution according to claim 7, wherein the concentration of CuSO₄.5H₂Ois 60-150 g/l, H₂SO₄ is 80-150 g/l, Cl⁻ ions are 50-150 ppm, andpolyethylene glycol is less than 100 ppm.